This invention relates to the field of optimisation of mobile data communication with mobility management. In particular, the invention relates to Quality of Experience optimisation using object caching for mobile data communication with mobility management.
A wireless mobile data terminal (the User Equipment (UE)) communicates with a server on a connected fixed network. A mobile data terminal may be any device that can send data over a wireless network where the network provides mobility management. Examples of networks include: the GPRS (General packet radio service) (2G) network; the WCDMA (Wideband Code Division Multiple Access) (3G) network; or the LTE (Long Term Evolution) or WiMAX (Worldwide Interoperability for Microwave Access) (4G) network. The background and description of the invention are described in terms of the 3rd Generation Mobile Phone Network, UMTS (Unified Mobile Telephony System)/WCDMA.
Referring to FIG. 1, a schematic diagram shows the UMTS architecture 100 which is standardised by the 3rd Generation Partnership Project (3GPP).
The wireless device, (cell phone, 3G dongle for a laptop, tablet device, etc.) is known in 3GPP terminology as a User Equipment (UE) 101. It connects wirelessly 110 to the base station which is labelled Base Station (BS) 102 and is known as a Node B in 3GPP terminology. Around 100 Node Bs are connected over microwave or optical fibre 120 to a Radio Network Controller (RNC) 103 which is connected back to a Serving GPRS Support Node (SGSN) 104 (which supports several RNCs) and then a Gateway GPRS Support Node (GGSN) 105. Finally the GGSN is connected back to the operators' service network (OSN) 10 which connects to the Internet 107 at a peering point.
The protocols between the base station back to the GGSN are various 3GPP specific protocols over which the IP traffic from the UE is tunnelled. Between the RNC 103 and the GGSN 105 a GPRS tunnelling protocol (GTP) 130 is used. Between the GGSN 105, OSN 106 and the Internet 107, standard Internet Protocol (IP) 140 is used. Note that the OSN 106 is termed the “Gi” reference point in the 3GPP terminology.
A key problem with communication via mobile networks is the rapid increase of data traffic. The density of mobile computing platforms is increasing at an exponential rate. Mobile computing platforms include traditional platforms such as phones, tablets and mobile broadband enabled laptops but increasingly also mobile data enabled devices, such as GPS systems, cars, even mobile medical equipment. This exponential increase brings significant new challenges for Mobile Network Operators (MNOs) as data becomes the majority of the content they deliver. Specifically although additional base stations are fairly easy to deploy to increase the available aggregate “air interface” bandwidth, the connections back from the base stations to the RNC, typically implemented as microwave links, are bandwidth constrained. Upgrading them to fibre optic connections is very expensive. Similarly increasing the available bandwidth in the RNC and core network is expensive.
The time taken to load a web page on a mobile device is typically much longer than to load the same page from a fixed connection. In part this is due to limited bandwidth and congestion in the network as described above but even if these factors are ignored, the round trip time over a mobile network is much longer than on a fixed link. Some of this increased round-trip delay time (RTT) is related to the radio interface from the UE to the base station and some is related to the connection back from the base station over microwave to the core network and the core network itself. Modifications being made to the air interface are improving the air interface latency: “evolved HSPA (High Speed Packet Access)” (sometimes informally described as 3.5G) and “Long Term Evolution” (informally described as 4G) but the latency through the microwave and core will persist.
Mobile Internet Optimisation.
One technique to address this is to “break out” the data traffic out of the mobile phone protocols and optimise it. Several companies market devices designed to break data traffic out of the network. Examples include the Mobile Data Offload (MDO) product from Stoke, Inc. and the Internet Offload appliance marketed by Continuous Computing. Each of these examples breaks traffic out of the 3GPP protocols at the RNC. Similar technology is emerging to break out the IP traffic at the base station.
Once the IP traffic has been broken out of the network, it is possible to put an optimisation platform at the edge of the mobile phone network, either at the RNC or in the base station. This platform can host various optimisation and other applications.
UMTS Mobility Management.
Referring to FIGS. 2A to 2C, a series of schematic block diagrams illustrate a network architecture 200 with mobility management as a user equipment (UE) 201 moves at the edge of the network. The figures show four base stations 211-214 named Node Bs. Sub-sets of base stations 211-212, 213-214 communicate with individual RNCs 221, 222. This communication is referred to as a backhaul link 231, 232 between the base stations and the core of the telephone company's network. The RNCs 221, 222 communicate with a SGSN 241 which uses a GGSN 251 which connects to the Internet 260 which includes multiple servers, such as the shown server 261. The server 261 has a TCP (Transmission Control Protocol) socket 262 which communicates with a TCP socket 202 at the UE 201 when a user wishes to access data from the server 261. In FIGS. 2A to 2C, the data transfer is shown in solid straight arrows, and the signalling control is shown as curved hashed arrows.
As mentioned earlier, the UMTS system makes a tunnel 270 from the GGSN 251 to the user equipment (UE) 201. In FIG. 1, the UE 201 is communicating with base station Node B 1 211 as the user is closest to this base station. The IP tunnel 270 is shown for user traffic. The IP tunnel 270 is shown for illustration purposes in FIGS. 2a to 2C and in practice passes through the interim components, such as the RNC 221 and the SGSN 241 in FIG. 2A.
As the UE 201 begins to move from one cell to the next, the RNC 221 detects movement of the UE 201 and starts a mobility event and works with the GSNs 251, 261 (GPRS Support Nodes) to move the tunnel 270 as the UE 201 moves from base station 211 to base station 212.
FIG. 2B shows the UE 201 moved to base station Node B 2 212 and the tunnel 270 moved correspondingly.
FIG. 2C shows the UE 201 moved to base station Node B 3 213 causing inter-RNC mobility as the UE 201 moves from a base stations with first RNC 1 221 to a base station with second RNC 2 222 with the tunnel 270 moved accordingly.
The key point is that the UMTS system maintains the integrity of the tunnel 270 across the mobility event. The TCP connections flowing through the tunnel 270 are not broken. It is possible that one or more IP packets may be dropped during the mobility event but TCP is designed to operate over lossy links and so this packet drop can be easily recovered.
As the UE continues to move, into an area served by a new RNC 222, the tunnel 270 is handed off seamlessly from one RNC 221 to another 222.
Traffic Optimisation Solutions Using Object Caching in the Base Station.
There are well known techniques to place a caching http forward proxy in the base station and to serve content from this. This approach achieves dramatic reductions in page load times for objects that are cached because objects can be cached taking a round trip back to the Gi or the server on the Internet. Each of these round trips can take 100 ms or more of which more than 60 ms can be saved. Since a typical page can contain tens of objects the cumulative effect of this latency is dramatic.
The problem with simply adding a caching forward http proxy at the base station is that it impacts on mobility management. The UE has a TCP connection which is terminated in the base station. If the UE moves to another base station, then it is extremely difficult to maintain a TCP connection which has state in a part of the network through which the data traffic is no longer travelling. There are some solutions in the literature which talk of forwarding traffic for these connections from the base station which the UE is using back to the base station where the TCP connection is terminated but this scheme has a number of drawbacks.
It requires an overlay network between base stations such that traffic can be forwarded from one base station to another. Management of this overlay is very difficult.
It uses up additional bandwidth to forward traffic from base station to base station and potentially increases the latency.